In later years electric machine designs evolved from modulated pole machines, claw pole machines, Lundell machines and transverse flux machines (TFM), have become more and more interesting. Electric machines using the principles of these machines were disclosed as early as about 1910 by Alexandersson and Fessenden.
One of the most important reasons for the increasing interest is that the design enables a very high torque output in relation to, for example, induction machines, switched reluctance machines and even permanent magnet brushless machines. Further, such machines are advantageous in that the coil often is easy to manufacture. However, one of the drawbacks of the design is that they are typically relatively expensive to manufacture and that they experience a high leakage flux, which decreases the performance and efficiency of the machine.